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Title: Collider Phenomenology of Extra Dimensions

Abstract

In recent years there has been much interest in the possibility that there exist more spacetime dimensions than the usual four. Models of particle physics beyond the Standard Model that incorporate these extra dimensions can solve the gauge hierarchy problem and explain why the fermion masses a spread over many orders of magnitude. In this thesis we explore several possibilities for models with extra dimensions. First we examine constraints on the proposal of Arkani-Hamed and Schmaltz that the Standard Model fermions are localized to different positions in an extra dimension, thereby generating the hierarchy in fermion masses. We find strong constraints on the compactification scale of such models arising from flavor-changing neutral currents. Next we investigate the phenomenology of the Randall-Sundrum model, where the hierarchy between the electroweak and Planck scales is generated by the warping in a five-dimensional anti-de Sitter space. In particular, we investigate the ''Higgsless'' model of electroweak symmetry breaking due to Csaki et. al., where the Higgs has been decoupled from the spectrum by taking its vacuum expectation value to infinity. We find that this model produces many distinctive features at the LHC. However, we also find that it is strongly constrained by precision electroweak observablesmore » and the requirement that gauge-boson scattering be perturbative. We then examine the model with a finite vacuum expectation value, and find that there are observable shifts to the Higgs scalar properties. Finally, in the original large extra dimension scenario of Arkani-Hamed, Dimopoulos, and Dvali, the hierarchy problem is solved by allowing gravity to propagate in a large extra dimensional volume, while the Standard Model fields are confined to 4 dimensions. We consider the case where there are a large number of extra dimensions (n {approx} 20). This model can solve the hierarchy problem without introducing a exponentially large radii for the extra dimensions, and represents a scenario that is difficult to obtain in string theory. We show that, if this scenario holds, the number of dimensions can be constrained to be larger than the number predicted by critical string theory. Searching for signals of many dimensions is then an important test of whether string theory is a good description of quantum gravity.« less

Authors:
;
Publication Date:
Research Org.:
Stanford Linear Accelerator Center (SLAC)
Sponsoring Org.:
USDOE
OSTI Identifier:
877224
Report Number(s):
SLAC-R-802
TRN: US200608%%150
DOE Contract Number:
AC02-76SF00515
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; ACCURACY; COMPACTIFICATION; DIMENSIONS; EXPECTATION VALUE; FERMIONS; NEUTRAL CURRENTS; PHYSICS; QUANTUM GRAVITY; SCALARS; SCATTERING; SPACE-TIME; STANDARD MODEL; SYMMETRY BREAKING; Phenomenology-HEP,HEPPH

Citation Formats

Lillie, Benjamin Huntington, and /Stanford U., Phys. Dept. /SLAC. Collider Phenomenology of Extra Dimensions. United States: N. p., 2006. Web. doi:10.2172/877224.
Lillie, Benjamin Huntington, & /Stanford U., Phys. Dept. /SLAC. Collider Phenomenology of Extra Dimensions. United States. doi:10.2172/877224.
Lillie, Benjamin Huntington, and /Stanford U., Phys. Dept. /SLAC. Fri . "Collider Phenomenology of Extra Dimensions". United States. doi:10.2172/877224. https://www.osti.gov/servlets/purl/877224.
@article{osti_877224,
title = {Collider Phenomenology of Extra Dimensions},
author = {Lillie, Benjamin Huntington and /Stanford U., Phys. Dept. /SLAC},
abstractNote = {In recent years there has been much interest in the possibility that there exist more spacetime dimensions than the usual four. Models of particle physics beyond the Standard Model that incorporate these extra dimensions can solve the gauge hierarchy problem and explain why the fermion masses a spread over many orders of magnitude. In this thesis we explore several possibilities for models with extra dimensions. First we examine constraints on the proposal of Arkani-Hamed and Schmaltz that the Standard Model fermions are localized to different positions in an extra dimension, thereby generating the hierarchy in fermion masses. We find strong constraints on the compactification scale of such models arising from flavor-changing neutral currents. Next we investigate the phenomenology of the Randall-Sundrum model, where the hierarchy between the electroweak and Planck scales is generated by the warping in a five-dimensional anti-de Sitter space. In particular, we investigate the ''Higgsless'' model of electroweak symmetry breaking due to Csaki et. al., where the Higgs has been decoupled from the spectrum by taking its vacuum expectation value to infinity. We find that this model produces many distinctive features at the LHC. However, we also find that it is strongly constrained by precision electroweak observables and the requirement that gauge-boson scattering be perturbative. We then examine the model with a finite vacuum expectation value, and find that there are observable shifts to the Higgs scalar properties. Finally, in the original large extra dimension scenario of Arkani-Hamed, Dimopoulos, and Dvali, the hierarchy problem is solved by allowing gravity to propagate in a large extra dimensional volume, while the Standard Model fields are confined to 4 dimensions. We consider the case where there are a large number of extra dimensions (n {approx} 20). This model can solve the hierarchy problem without introducing a exponentially large radii for the extra dimensions, and represents a scenario that is difficult to obtain in string theory. We show that, if this scenario holds, the number of dimensions can be constrained to be larger than the number predicted by critical string theory. Searching for signals of many dimensions is then an important test of whether string theory is a good description of quantum gravity.},
doi = {10.2172/877224},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Fri Mar 10 00:00:00 EST 2006},
month = {Fri Mar 10 00:00:00 EST 2006}
}

Technical Report:

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  • We study the phenomenology of a supersymmetric bulk in the scenario of large extra dimensions. The virtual exchange of gravitino KK states in selectron pair production in polarized e{sup +}e{sup -} collisions is examined. The leading order operator for this exchange is dimension six, in contrast to that of graviton KK exchange which induces a dimension eight operator at lowest order. Some kinematic distributions for selectron production are presented. These processes yield an enormous sensitivity to the fundamental higher dimensional Planck scale.
  • No abstract prepared.
  • A recent suggestion that quantum gravity may become strong near the weak scale has several testable consequences. In addition to probing for the new large (submillimeter) extra dimensions associated with these theories via gravitational experiments, one could search for the Kaluza Klein towers of massive gravitons which are predicted in these models and which can interact with the fields of the Standard Model. Here we examine the indirect effects of these massive gravitons being exchanged in fermion pair production in e{sup +}e{sup {minus}} annihilation and Drell-Yan production at hadron colliders. In the latter case, we examine a novel feature ofmore » this theory, which is the contribution of gluon gluon initiated processes to lepton pair production. We find that these processes provide strong bounds, up to several TeV, on the string scale which are essentially independent of the number of extra dimensions. In addition, we analyze the angular distributions for fermion pair production with spin-2 graviton exchanges and demonstrate that they provide a smoking gun signal for low-scale quantum gravity which cannot be mimicked by other new physics scenarios.« less
  • The elementary particles of the Standard Model may live in more than 3+1 dimensions. We study the consequences of large compactified dimensions on scattering and decay observables at high-energy colliders. Our analysis includes global fits to electroweak precision data, indirect tests at high-energy electron-positron colliders (LEP2 and NLC), and direct probes of the Kaluza-Klein resonances at hadron colliders (Tevatron and LHC). The present limits depend sensitively on the Higgs sector, both the mass of the Higgs boson and how many dimensions it feels. If the Higgs boson is trapped on a 3+1 dimensional wall with the fermions, large Higgs massesmore » (up to 500 GeV) and relatively light Kaluza-Klein mass scales (less than 4 TeV) can provide a good fit to precision data. That is, a light Higgs boson is not necessary to fit the electroweak precision data, as it is in the Standard Model. If the Higgs boson propagates in higher dimensions, precision data prefer a light Higgs boson (less than 260 GeV), and a higher compactification scale (greater than 3.8 TeV). Future colliders can probe much larger scales. For example, a 1.5 TeV electron-positron linear collider can indirectly discover Kaluza-Klein excitations up to 31 TeV if 500 fb{sup {minus}1} integrated luminosity is obtained.« less
  • We review the capability of colliders to detect the virtual exchange of Kaluza-Klein towers of gravitons within the low scale quantum gravity scenario of Arkani-Hamed, Dimopoulos and Dvali.